In a corrugated fiberboard carton wall, the primary function of the fluting medium is to space apart the face liners and provide resistance to flat crush loads normal to the planes of the face liners. This flat crush resistance also plays a part in resisting end loading on the box wall in that flat crush resistance helps resist buckling due to column loading on the wall.
Conventional fluting patterns suffer an inherent shortcoming in that increased flute height, which is desired for increased wall thickness and resistance to buckling, reduces flat crush resistance because of the greater unsupported length of the medium from one face to the other. In addition to column height of the medium, flute tip radius and flute angle affect the wall strength. A discussion of the effect of flute tip radius and flute angle on strength can be found in an article by D. K. Chow, Design of cost effective flute features in corrugating medium, Tappi Journal, pp 126-128, October 1986.
Variability of flute tip radius and flute angle in conventional practice is limited by the conditions in the labyrinth formed by converging corrugator rolls as the flutes are being formed in the fluting (or corrugating) medium. A discussion of this factor may be found in an article by John R. Sofinowski, Trends in high-speed single facer design, Tappi Journal, pp 43-47, October 1987. This labyrinth creates a distinct limitation on the flute profile obtainable in presently known corrugators.
A discussion of the behavior of symmetrical fluting under flat crush loading is found in an article by Jen Y. Liu, Flat-crush failure mechanism of corrugated fiberboard, Journal of Applied Mechanics, 53 (9): 602-608 (1986). FIG. 12 in the article is especially pertinent.
Rodgers, Jr., in U.S. Pat. No. 2,973,295, teaches a corrugated fiberboard in which one or both sides of the fluted medium are entirely filled with an expanded foam. This is done to improve dry strength and crush resistance.
Blandy, in U.S. Pat. No. 3,691,002, shows a corrugated fiberboard strengthened by coating all interior surfaces with a liquid resin to increase stiffness and crush resistance.